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//! Reading/writing events from/to Apache Kafka servers.
use std::convert::TryInto;
use std::io;
use kafka::consumer::{Consumer, FetchOffset, GroupOffsetStorage};
use kafka::producer::{Producer, Record, RequiredAcks};
use rmp_serde::Serializer;
use serde::Serialize;
use crate::fluentd::{Entry, ForwardMode};
use crate::Error;
/// An event included in a Kafka message at `loc`.
#[derive(Debug)]
pub struct Event {
pub entry: Entry,
pub loc: EntryLocation,
}
impl crate::Event for Event {
type Ack = EntryLocation;
fn raw(&self) -> &[u8] {
self.entry
.record
.get("message")
.map_or(b"", |v| v.as_slice())
}
fn time(&self) -> super::SeqNo {
super::SeqNo::from_ne_bytes(self.entry.time.to_ne_bytes())
}
fn ack(&self) -> Self::Ack {
self.loc
}
}
/// The location of an event on a Kafka topic.
#[derive(Copy, Clone, Debug)]
pub struct EntryLocation {
remainder: u32, // # of entries in the message after this entry
partition: i32,
offset: i64,
}
/// Event reader for Apache Kafka.
pub struct Input {
data_channel: Option<crossbeam_channel::Sender<Event>>,
ack_channel: crossbeam_channel::Receiver<EntryLocation>,
consumer: Consumer,
fetch_limit: usize,
}
impl Input {
/// Creates `Input` that fetches at most `fetch_limit` entries from the
/// given Kafka topic.
///
/// # Errors
///
/// Returns an error if it fails to connect to Kafka as a consumer.
pub fn new(
data_channel: crossbeam_channel::Sender<Event>,
ack_channel: crossbeam_channel::Receiver<EntryLocation>,
hosts: Vec<String>,
group: String,
client_id: String,
topic: String,
fetch_limit: usize,
) -> Result<Self, kafka::Error> {
let consumer = Consumer::from_hosts(hosts)
.with_group(group)
.with_fallback_offset(FetchOffset::Earliest)
.with_fetch_max_bytes_per_partition(1_000_000)
.with_offset_storage(Some(GroupOffsetStorage::Kafka))
.with_client_id(client_id)
.with_topic(topic)
.create()?;
Ok(Self {
data_channel: Some(data_channel),
ack_channel,
consumer,
fetch_limit,
})
}
}
impl super::Input for Input {
type Data = Event;
type Ack = EntryLocation;
/// Reads events from Kafak and forwards them through `data_channel`.
///
/// # Errors
///
/// Returns an error if it cannot fetch messages from Kafka, receives an
/// invalid message, or receives an invalid ACK from `ack_channel`.
fn run(mut self) -> Result<(), Error> {
let Some(data_channel) = &self.data_channel else {
return Err(Error::ChannelClosed);
};
let mut sel = crossbeam_channel::Select::new();
let send_data = sel.send(data_channel);
let recv_ack = sel.recv(&self.ack_channel);
'poll: loop {
let messagesets = self
.consumer
.poll()
.map_err(|e| Error::CannotFetch(Box::new(e)))?;
if messagesets.is_empty() {
break 'poll;
}
for msgset in messagesets.iter() {
let partition = msgset.partition();
for msg in msgset.messages() {
let fwd_msg: ForwardMode = rmp_serde::from_slice(msg.value)
.map_err(|e| Error::InvalidMessage(Box::new(e)))?;
if fwd_msg.entries.len() > u32::MAX as usize {
return Err(Error::TooManyEvents(fwd_msg.entries.len()));
}
let (remaining, overflow) =
self.fetch_limit.overflowing_sub(fwd_msg.entries.len());
if overflow {
break 'poll;
}
self.fetch_limit = remaining;
let offset = msg.offset;
for (remainder, entry) in (0..fwd_msg.entries.len()).rev().zip(fwd_msg.entries)
{
loop {
let oper = sel.select();
match oper.index() {
i if i == send_data => {
let event = Event {
entry,
loc: EntryLocation {
remainder: remainder
.try_into()
.expect("remainder <= u32::MAX"),
partition,
offset,
},
};
if oper.send(data_channel, event).is_err() {
// data_channel was disconnected. Exit the
// loop and commit consumed.
break 'poll;
}
break;
}
i if i == recv_ack => {
let Ok(ack) = oper.recv(&self.ack_channel) else {
// ack_channel was disconnected. Exit the
// loop and commit consumed.
break 'poll;
};
handle_ack(
&self.ack_channel,
&mut self.consumer,
msgset.topic(),
&ack,
)?;
}
_ => unreachable!(),
}
}
}
}
}
}
self.data_channel = None;
let subs = self.consumer.subscriptions();
let topic = subs.keys().next().expect("subscribes to one topic");
for ack in &self.ack_channel {
handle_ack(&self.ack_channel, &mut self.consumer, topic, &ack)?;
}
Ok(())
}
}
fn handle_ack(
ack_channel: &crossbeam_channel::Receiver<EntryLocation>,
consumer: &mut Consumer,
topic: &str,
ack: &EntryLocation,
) -> Result<(), Error> {
if ack.remainder == 0 {
consumer
.consume_message(topic, ack.partition, ack.offset)
.map_err(|e| Error::Fatal(format!("messages from Kafka have different topics: {e}")))?;
}
if ack_channel.is_empty() {
consumer
.commit_consumed()
.map_err(|e| Error::CannotCommit(Box::new(e)))?;
}
Ok(())
}
/// Event writer for Apache Kafka.
pub struct Output<T> {
data_channel: crossbeam_channel::Receiver<T>,
producer: Producer,
topic: String,
}
impl<T> Output<T>
where
T: std::fmt::Debug + Into<ForwardMode> + Serialize,
{
/// Creates an event writer for Apache Kafka.
///
/// # Errors
///
/// Returns an error if it fails to connect to Kafka as a consumer.
pub fn new(
data_channel: crossbeam_channel::Receiver<T>,
hosts: Vec<String>,
topic: String,
) -> Result<Self, kafka::Error> {
let producer = Producer::from_hosts(hosts)
.with_required_acks(RequiredAcks::One)
.create()?;
Ok(Self {
data_channel,
producer,
topic,
})
}
/// Sends messages received through `data_channel` to Kafka.
///
/// # Errors
///
/// Returns an error if message serialization or transmission fails.
pub fn run(&mut self) -> Result<(), kafka::Error> {
let mut buf = Vec::new();
for msg in &self.data_channel {
msg.serialize(&mut Serializer::new(&mut buf))
.map_err(|e| kafka::Error::Io(io::Error::new(io::ErrorKind::InvalidData, e)))?;
self.producer
.send(&Record::from_value(&self.topic, buf.as_slice()))?;
buf.clear();
}
Ok(())
}
}